Biomedical subjects

M D MacNeil

Publications and source records attributed to M D MacNeil.

53 records · Page 3Linked to original sources

PubMed1996

Systematic error in genetic evaluation of miles city line 1 hereford cattle resulting from preadjustment for age of dam.

Differences in preweaning growth of calves nursing 2- and 3-yr-old dams compared with contemporaries nursing older dams are accentuated in the Miles City Line 1 Hereford herd relative to age-of-dam (AOD) effects implied by preadjustment of 205-d weight in national cattle evaluation. Mixed-model analyses of 205-d weight that fit random individual direct effects and maternal genetic and permanent environmental effects on 4,998 calves were conducted to 1) determine the magnitude of residual AOD effects after preadjustment (PA) using industry-standard procedures and 2) compare changes in genetic predictions resulting from either PA or simultaneous adjustment (SA) for AOD. Expressed as differences from the 5- to 10-yr-old age effect, simultaneously estimated AOD effects were 45 +/- 1, 19 +/- 1, 6 +/- 1, and 19 +/- 3 kg for 2, 3, 4, and 11+ AOD classes, respectively. Comparable estimates of residual AOD effects after PA were 20 +/- 1, 6 +/- 1, 1 +/- 1, and 14 +/- 3 kg. Rank correlations of direct (BVd) and maternal (BVm) breeding values (BV) for 205-d weight from the analysis using PA with BV predicted using SA for AOD were .98 and .77, respectively. Estimated genetic trends were also affected by the method of accounting for AOD effects. One hundred fifty replicate simulations of 205-d weights with pedigree, fixed effect, and variance-covariance structures corresponding to the experimental population were used to establish correlations (r) of predicted BV with underlying true values. The r of predicted BVd with true values were reduced less than .02 by PA compared to SA in accounting for AOD. However, r of predicted BVm with true values were reduced more than .13 by PA compared to SA in accounting for AOD. These data indicate potential for systematic error in genetic evaluations that apply standard adjustments for AOD to 205-d weight.

Aging↗

PubMed1995

Development and evaluation of a regression equation of prediction for fat-free soft tissue in heterogenous populations of cattle.

Regression equations to predict kilograms of fat-free soft tissue (the sum of water and protein from chemical analyses) were developed from data collected on 526 steers and heifers. Straightbred animals representing Angus, Braunvieh, Charolais, Gelbvieh, Hereford, Limousin, Pinzgauer, Red Poll, and Simmental breeds of cattle contributed to the data set. Cattle ranged in slaughter weight and age from approximately 350 to 575 kg and from 13 to 23 mo, respectively. Diets (100% ground alfalfa, 67% ground alfalfa and 33% ground corn or 33% ground alfalfa and 67% ground corn) were cross-classified with breed and sex. Estimative traits included in the equation were warm carcass weight, fat depth at the 12th rib, and body impedance. Carcass soft-tissue samples were taken for determination of chemical constituents. The prediction equation accounted for 94% of the variation in fat-free soft tissue of the carcass. Adjusting for breed-sex-diet contemporary groups increased the R2 value by 2% units. The prediction model was evaluated using data collected on 65 steers sired by Charolais or by Hereford bulls at the Ft Keogh Livestock and Range Research Laboratory (Miles City, MT). Postweaning feeding strategies and slaughter ages varied among these animals. Carcass weight, back fat depth, and resistive impedance measures were recorded. Carcass soft-tissue samples were taken for determination of chemical constituents. Values of estimator variables recorded at Ft. Keogh were used in the regression equation to predict fat-free soft tissue for each animal. The values for kilogram of fat-free soft tissue determined from chemical analysis were regressed on predicted fat-free soft tissue. the results indicate that fat-free soft tissue of carcasses can be accurately predicted using estimative traits that do not diminish carcass value.

Animals↗

PubMed1994

Genetic analysis of calving date in Miles City Line 1 Hereford cattle.

A model for genetic analysis of calving date was proposed and variance components, genetic trends, and fixed effects for calving date were estimated in the Miles City Line 1 Hereford cattle population. There were 951 pedigree records that predated 1935, when data collection began, and 4,692 subsequent recorded calving dates through 1989. The statistical model included fixed linear continuous effects for inbreeding of calf and inbreeding of dam, discrete fixed effects for year, sex of calf, and age and previous parity of dam, and random sources of variation for individual (calf) and maternal additive genetic effects, and environmental effects of dams, mating groups, and residuals. All effects were estimated simultaneously by derivative-free procedures for REML. Male calves were born 1.58 +/- .40 d later than female calves. Cows failing to wean a calf in the previous year calved 2.81 +/- .81 d earlier than cows that had weaned a calf. Other fixed effects were small. Variance components (d2) were 23.0 for individual additive genetic effects, 5.8 for maternal additive genetic effects, 9.2 for maternal permanent environmental effects, 11.8 for contemporary group effects, and 161.3 for residual effects. Environmental trend was +.17 d/yr and individual additive genetic trend was -.07 d/yr. No maternal additive genetic trend was detected. These results do not encourage the use of calving day as a selection criterion for improving fertility of beef cattle.

Animals↗

PubMed1994

Evaluation of cytoplasmic genetic effects in Miles City Line 1 Hereford cattle.

Mixed-model techniques were used to evaluate the importance of cytoplasmic genetic effects on growth traits in beef cattle. The data used were records on birth weight (BWT, n = 4,716), preweaning average daily gain (PREADG, n = 4,428), and postweaning average daily gain (POSTADG, n = 3,476) collected from 1935 through 1989 in a closed line of Hereford cattle (Miles City Line 1). Selection criterion was adjusted yearling weight. Cytoplasmic genetic effects were evaluated as both potential fixed and random genetic effects. Cytoplasmic sources (n = 26) were determined based on the foundation female in the maternal lineage of each animal. All foundation females were at least five generations removed from any descendant that produced a performance record. An animal model was used to account for all nuclear additive genetic variation among animals. Direct additive effects were estimated for all traits. Maternal additive and permanent environmental effects were estimated for BWT and PREADG. Fixed effects included year of birth, age of dam, sex of calf, and regressions on inbreeding of calf, inbreeding of dam, and age off postweaning gain test (POSTADG only). When cytoplasm was fit as a fixed effect, F-tests for cytoplasmic effects were not significant (P = .10 to .99) for any trait. Inclusion of cytoplasmic source (fixed) in the statistical model reduced residual standard deviations less than .1%. Variance components for cytoplasmic genetic effects were estimated simultaneously with variance components for direct, maternal, direct-maternal covariance, and maternal permanent environment using REML techniques. Cytoplasmic source accounted for .40, .00 and .00% of the phenotypic variance for BWT, PREADG, and POSTADG, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Fixed effects in the formation of a composite line of beef cattle: I. Experimental design and reproductive performance.

Red Angus (RA) dams were mated to Charolais (C) or Tarentaise (T) sires to produce crossbred (F1) progeny. Members of the F1 generation, differing in breed direct effects, were mated to produce an F2 generation with an expected breed composition of 1/2 RA, 1/4 C, and 1/4 T. Two breed groups within the F2 generation differing in breed maternal effect ([C x RA] x [T x RA] and [T x RA] x [C x RA]) were identified separately. These breed groups were crossed to produce an F3 generation and, likewise, the two resulting F3 generation breed groups were crossed to produce an F4 generation. No distinction was made among breed groups subsequent to the F3 generation. Pregnancy rates averaged 90.9% over 11 yr, with 82.0% of cows exposed weaning a calf. Among formative generations of this composite population, F2 had greatest pregnancy, calving, and weaning rates. Age of dam significantly affected pregnancy rate, calving difficulty, and gestation length. Older cows tended to express higher pregnancy rates and longer gestation lengths than did younger cows (P < .01). Males calves had a 1.7% greater weaning rate than female calves (P < .05), but matings producing male calves had longer gestation lengths (P < .05) and were 8.5% more likely to experience calving difficulty (P < .01). Individual breed additive effects (calves from C or T sires mated to RA dams) were important for calving difficulty only (P < .05), where C-sired matings experienced greater calving difficulty. Differences between C x RA and T x RA dams, indicative of maternal breed additive effects, were not detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1993

Fixed effects in the formation of a composite line of beef cattle: II. Pre- and postweaning growth and carcass composition.

Generation, age of dam, sex of calf, and certain covariates were studied to elucidate their effect on traits related to growth and carcass characters measured on individuals from a stabilized three-breed composite (1/2 Red Angus [RA], 1/4 Charolais [C], 1/4 Tarentaise [T]). There was evidence that sires had been selected for yearling weight. Thus, an animal model was fitted to the data to estimate the effects free of bias due to selection. Differences between generations were not different from zero (P > .05) for birth weight, weaning weight, and preweaning ADG. There were few important differences between generations for carcass traits as well. This may have been caused by confounding of individual and maternal heterotic effects with direct and maternal components of the model, or the partial confounding of years, age of dam, and generation. Birth weight was curvilinear with respect to calving day (P < .01). Age of dam was important for all growth traits except postweaning ADG. In general, growth of calves increased with increasing age of dam, as did carcass weight and predicted retail product. Individual breed additive effects (differences between calves sired by C and T sires mated to RA dams) were positive for birth weight (P < .01), weaning weight (P < .05), carcass weight (P < .05), and predicted retail product (P < .05). Maternal breed additive effects (differences between calves out of C x RA or T x RA dams) were also positive for weaning weight (P < .05), carcass weight (P < .05), and fat depth (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1992

Selection for postweaning growth in inbred Hereford cattle: the Fort Keogh, Montana line 1 example.

Demographic characteristics and genetic trends in birth weight and pre- and postweaning ADG were examined in a population of Hereford cattle (Line 1). Line 1 was founded largely from two paternal half-sib sires and has been selected for postweaning growth. There were pedigree records on 951 members of the base population that predated 1935, when data collection began. Numbers of records analyzed using mixed-model methodology were 4,716 birth weight, 4,427 preweaning ADG, and 3,579 postweaning ADG. Birth weight and preweaning ADG were considered to have direct and maternal genetic components. Inbreeding accumulated rapidly from 1935 to 1960 and more slowly (.22%/yr) thereafter. Any reduction in additive genetic variance due to inbreeding and selection may have been offset by a concurrent reduction in generation interval that was observed as time progressed. Expected selection differential for 365-d weight, averaged over sexes, was 31.2 kg per generation. For birth weight, annual genetic trends in direct and maternal effects were 42 +/- 3 g and 15 +/- 3 g, respectively. Annual direct and maternal genetic trends for preweaning ADG were .70 +/- .06 g/d and .63 +/- .06 g/d, respectively. Direct response in postweaning ADG was linear and equal to 5.3 +/- .6 g.d-1.yr-1. As a result, estimated breeding values of birth weight, 200-d weight, and 365-d weight increased by 3.2 kg, 14.5 kg, and 62.4 kg, respectively, from 1935 to 1989. Selection within Line 1 was effective in increasing genetic potential for growth over 13 generations. No selection plateau was observed in any of the traits examined.

Age Factors↗

PubMed1991

Maternal breed of sire effects on postweaning performance of first-cross heifers and production characteristics of 2-year-old heifers.

Postweaning growth rates from weaning to 18 mo, fall condition score, pregnancy rates, and production to 2 yr of age were evaluated in a study of Angus (A)-, Pinzgauer (P)-, Red Poll (R)-, Simmental (S)-, and Tarentaise (T)-sired females from Hereford dams. First-cross heifers from the different sire breeds did not differ (P greater than .10) in initial weight. During a 140-d feed test, S gained 98.6 kg, exceeding (P less than .05) gains of P, 92.3; A, 91.4; and R, 87.3 kg but not T, 94.1 kg. Red Poll-sired heifers weighed less at the end of the 140-d test (P less than .05) than the other crosses, which did not significantly differ from each other. No breed of sire differences were found in gain from 140 d to fall weight. Simmental-sired heifers weighed more (P less than .05) than A- and R-sired heifers at 18 mo. Breed of sire and year interacted to affect pregnancy rate of the yearling heifers when mated to Shorthorn sires for 45 d. Percentage of dystocia varied from a low of 26.3 and 28.9% for T- and A-sired heifers, respectively, to 54.4 and 60.8% for P- and S-sired heifers, respectively (P less than .05). Age of dam of heifers affected (P less than .05) weight at the different period end points but not gains after weaning. Age of dam also affected incidence of dystocia. Two-year-old heifers from young dams had more dystocia than heifers from older dams. Shorthorn-sired calves from 2-yr-old heifers with different sire breeds differed in birth weight (P less than .05) but not survival from birth to weaning, ADG from birth to weaning, weaning age, or weaning condition score. Average 200-d weight of calves from P-, S- and T-sired heifers exceeded those from A- and R-sired heifers by 10.7 kg, or 5.7%.

Animals↗

PubMed1991

Biological type effects on postweaning growth, feed efficiency and carcass characteristics of steers.

Postweaning growth, feed consumption and carcass characteristics of 259 individually fed F1 Angus-, Red Poll-, Pinzgauer-, Simmental- and Tarentaise-sired steers from Hereford dams were compared. Average daily gain to 382 d of age for Simmental-sired steers exceeded (P less than .05) the ADG for Red Poll, Angus and Pinzgauer, which were not different. Tarentaise-sired steers were intermediate in growth rate. Simmental-sired steers required less (P less than .05) feed per kilogram of gain than Red Poll- and Angus-sired steers to reach either 382 d of age or 400 kg. Feed conversion (FC) by Simmental, Pinzgauer and Tarentaise-sired steers did not differ (P greater than .05), nor did FC by Red Poll- and Angus-sired steers to reach 382 d or 400 kg. Angus-sired steers required less ME per kilogram of gain to reach 12.7 mm of carcass backfat than did Red Poll-, Pinzgauer- or Tarentaise-sired steers, which were similar. Simmental-sired steers were intermediate in feed conversion to 12.7-mm fat depth and did not differ from the other breed groups. Rankings of breed groups for traits indicative of lean tissue growth were similar to rankings for live animal growth traits. At age- and weight-constant endpoints, Angus-sired steers had more (P less than .05) fat cover and marbling than did steers sired by the other breeds. At these endpoints, Red Poll-sired steers also had more (P less than .05) fat cover than did Pinzgauer-, Simmental- and Tarentaise-sired steers, which were similar.

Adipose Tissue↗

PubMed1991

Heritabilities and genetic correlations for postweaning growth and feed intake of beef bulls and steers.

Data from studies conducted at Miles City, MT and Lethbridge, AB were pooled to evaluate genetic and environmental variation in feed intake (MEI), growth rate (ADG), MEI-to-gain ratio (M/G), final weight (FWT), and fat thickness (FAT). A total of 124 sires with an average of 4.25 progeny each were represented in the data. Restricted maximum likelihood methods were used to estimate within and between paternal half-sib estimates of variance and covariance. Heritabilities and genetic, phenotypic, and environmental correlations with inference to populations at 365 d of age were calculated from the estimates. Heritabilities were as follows: ADG, .38 +/- .16; MEI, .45 +/- .17; M/G, .26 +/- .15; FWT .25 +/- .15; and FAT .52 +/- .17. The genetic correlation of MEI with ADG was large (.73 +/- .13) and antagonistic to genetic improvement of M/G through selection for ADG. Efficient genetic improvement in M/G was found to depend on using either MEI or an indicator of composition of gain as selection criteria in addition to ADG. Selection to improve M/G using an index that included FWT and FAT, in addition to MEI and ADG, resulted in greater predicted response in ADG and lesser predicted response in MEI than the index of ADG and MEI alone.

Adipose Tissue↗

PubMed1989

Effects of inbreeding and heterosis in Hereford females on fertility, calf survival and preweaning growth.

Effects of inbreeding and heterosis and the difference between them were estimated by comparing linecross (L), topcross (T), inbred (I) and control line (C) Hereford females for reproductive and preweaning growth traits of their progeny. Inbred females (average inbreeding coefficient = 26.5%) originated from four single-sire inbred lines. Control females (average inbreeding coefficient = 6.9%) were produced by a four-sire, 60-cow line. Linecross females were produced from all possible reciprocal crosses of the I lines. Topcross females were produced by mating I bulls to C cows. Differences in pregnancy rate among these lines were not detected. Effects of maternal heterosis were positive for both prenatal and postnatal survival. The weaning rate by L females exceeded the weaning rate by I females as a result. Prenatal survival was reduced in calves from I females relative to those from C females, resulting in corresponding differences in birth and weaning rates. Differences in the magnitudes of maternal heterosis and inbreeding effects were not detected, except for birth weight. For birth weight the effect of maternal inbreeding was of greater magnitude than the effect of maternal heterosis. Within the I and C lines regressions of pregnancy rate, prenatal survival, birth rate, postnatal survival, weaning rate, weaning weight/cow exposed, birth weight and weaning weight on the inbreeding coefficients of the cows indicated significant inbreeding depression on all traits except pregnancy rate and postnatal survival.

Animals↗

PubMed1986

Variables in estimation of adipocyte size and number with a particle counter.

Porcine adipose tissue slices were fixed with osmium tetroxide and cells released by treatment with urea. Cell size and number were determined by an instrumental method using a particle counter. Storage of adipose tissue samples as frozen slices or in osmium, in post-osmium saline, in urea or in post-urea Triton all tended to produce less acceptable results than obtained with fresh tissue slices. Various storage conditions either tended to diminish cell size, to produce small particles or to cause aggregation. Repeatabilities of cell number, cell diameter and cell volume from multiple samples obtained from one anatomical location within an animal (perfect repeatability = 1) were .39, .52 and .65, respectively. Repeatabilities of instrument determinations were greater than .98 for cell number, cell diameter and cell volume. Cell number may be estimated from particle counts or indirectly from average size. Particle count number and that calculated from mean cell diameter were similar, whereas cell numbers estimated from mean cell volumes were smaller. Different adipose tissue depots and backfat layers had divergent cell size, making extrapolation to whole-animal cell number complex.

Adipose Tissue↗

PubMed1986

Between- and within-breed genetic analysis of calving traits and survival to weaning in beef cattle.

Data for gestation length, birth weight, calving difficulty (percent assisted) and survival from birth to weaning were analyzed from 4,639 calves by 290 sires of 14 Bos taurus breeds (Hereford, Angus, Jersey, South Devon, Limousin, Simmental, Charolais, Red Poll, Brown Swiss, Gelbvieh, Maine Anjou, Chianina, Pinzgauer and Tarentaise) mated to Hereford and Angus cows. The calves were produced over a 7-yr period in a germ plasm evaluation program. Variance components were estimated for breed of sire (sigma 2b), sire within breed of sire (sigma 2s) and progeny within sire (sigma 2w) random effects. Estimates of sigma 2b and sigma 2s direct genetic variance were similar for gestation length and calf survival. Estimates of sigma 2b genetic variance were greater than for sigma 2s for birth weight and calving difficulty. Estimates of total heritability [h2t = 4(sigma 2b + sigma 2s)/(4 sigma 2b + sigma 2s + sigma 2w)] and within-breed heritability (h2w = 4 sigma 2s/sigma 2s + sigma 2w) indicated that gestation length (h2t = .77, h2w = 64) and birth weight (h2t = .79, h2w = .46) are under a high degree of direct genetic control, calving difficulty (h2t = .42, h2w = .21) is under a moderate degree of direct genetic control and calf survival (h2t = .11, h2w = .07) is under a low degree of direct genetic control. Estimates of genetic correlation for between (rb) - and within-breed (rg) sources of genetic variation were comparable in direction, but tended to be stronger between than within breeds.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Relationship of plasma lipid concentrations to fat deposition in pigs.

The time course for changes in plasma free fatty acid and triglyceride concentration after removal of feed was established. Genetically obese and lean lines of pigs, two types of crossbred female pigs and a group of male pigs were used to establish the relationship between circulating free fatty acid or triglyceride concentrations and adiposity. Pigs were weighed, ultrasonically probed for backfat thickness, bled in a fed state and again in the fasted state. Plasma was analyzed for free fatty acid and triglyceride concentration. Fasting increased plasma free fatty acid, but only slightly increased triglyceride concentrations. There were several significant correlations between backfat thickness and plasma lipid concentrations; however, the low magnitude and inconsistency of these correlations precludes use of plasma lipid concentrations as indicators of adiposity in swine. Fasted obese pigs had lower plasma fatty acid concentrations than lean pigs at 2, 4 and 6 mo of age. If these plasma levels represent in vivo mobilization of fat, the results probably contrast with previously reported in vitro results wherein adipose tissue from obese pigs had lipolytic rates expressed on a cellular basis that were equal to or greater than those form lean pigs.

Adipose Tissue↗

PubMed1984

Genetic correlations among sex-limited traits in beef cattle.

Data from a comprehensive germ plasm evaluation program were used to estimate genetic correlations of reproductive and maternal traits of beef females with growth and carcass traits of their steer paternal half-sibs. The data set consisted of 187 sires with approximately four female and five male progeny each. Heritability estimates for age at puberty, weight at puberty, conceptions/service, gestation length, calving difficulty, progeny birth weight, progeny preweaning daily gain and mature weight measured on females were .613 +/- .177, .700 +/- .114, .026 +/- .126, .298 +/- .175, .217 +/- .175, .374 +/- .174, .094 +/- .161, and .540 +/- .150, respectively. Postweaning daily gain, carcass weight, fat trim weight and retail product weight measured on male half-sibs had estimated heritabilities of .363 +/- .090, .441 +/- .093, .502 +/- .093 and .451 +/- .093, respectively. The estimated genetic correlations suggest that selection for postweaning daily gain would result in increased age and weight at puberty, increased mature weight, improved fertility, reduced maternal gestation length, reduced maternal calving difficulty, increased maternal birth weight and reduced maternal preweaning gain. Predicted correlated responses to selection for reduced fat trim at a constant age were increased age and weight at puberty, increased mature weight, reduced maternal fertility, reduced maternal preweaning gain and increased maternal gestation length, birth weight and calving difficulty. Consequences of selection for increased age constant retail product weight or carcass weight appear to be increased age and weight at puberty, increased mature weight, improved fertility, increased maternal gestation length and maternal birth weight but reduced maternal difficulty and reduced maternal preweaning gain.

Animals↗

PubMed1983

Improvements to the mathematical description of prenatal growth.

The exponential form of growth was used to describe prenatal growth in mouse, rat, guinea pig, swine, sheep, cattle and man. Instantaneous growth rate was permitted to vary as a function of time and, in litter bearing species, number of fetuses. Models for which instantaneous growth rate decreased linearly in time had a tendency to overestimate fetal weight from mid-gestation until midway through the last trimester of pregnancy and subsequently, underestimate fetal weight. When instantaneous growth rate varied as a quadratic function of time, a more accurate and precise prediction of fetal weights resulted.

Animals↗

PubMedDate not supplied

The "spotted" locus maps to bovine chromosome 6 in a Hereford-Cross population.

The spotted locus is responsible for several phenotypically distinguishable piebald patterns in cattle, including Hereford, or white face (SH), lineback (SP), and recessive spotting (s), in addition to nonspotted (S+). In a backcross mapping population, the S locus has been mapped by genetic linkage to bovine chromosome 6, between microsatellite markers BM4528 and EL03. This region corresponds comparatively to a region on mouse chromosome 5 which houses several coat color mutations, among which homology is possible with Hardy-Zuckerman 4 feline sarcoma viral oncogene homologue (Kit), patch (Ph), and rump white (Rw). Mutations at these loci resemble mutations at the bovine S locus in both phenotype and mode of inheritance. Data are presented which show genetic linkage between the bovine S locus and microsatellite markers on chromosome 6. Candidate genes for the bovine S locus are discussed.

Animals↗